The present invention generally relates to structures that provide electrical contacts only from a backside of a multi-junction photovoltaic cell in order to increase an effective area of the photovoltaic cell, and methods of manufacturing the same.
A photovoltaic cell is a device that converts light directly into electricity by the photovoltaic effect. Assemblies of photovoltaic cells are used to make solar panels, solar modules, or photovoltaic arrays. A photovoltaic cell can be formed by providing a large area p-n junction in a semiconductor material.
A space charge region is formed around a p-n junction in a photovoltaic cell. Photons that impinge on the space charge region generate at least one electron-hole pair if absorbed by the semiconductor material in the space charge region. The electrons and holes diffuse in opposite directions, thereby accumulating positive charges in the bulk portion of the p-doped material and accumulating negative charges in the bulk portion of the n-doped material.
Conventional photovoltaic cells are configured to provide a p-doped region on one side of the cell and an n-doped region on the opposite side of the cell. For example, the front side of the cell can be the p-doped region and the back surface of the cell can be the n-doped region, or vice versa. First electrical contacts are made to one node of the photovoltaic cell from the front side, and second electrical contacts are made to the other node of the photovoltaic cell from the back surface. Because the electrical contacts on the front side need to be wired together, a one dimensional array of metal lines is provided on the front side of conventional photovoltaic cells. Such metal lines are called “grid lines” on a photovoltaic cell.
However, such gird lines block a significant portion of the front side of the photovoltaic cell, thereby reducing the effective area of the photovoltaic cell. Moreover, the width of grid lines on the front side cannot exceed a threshold width in order to limit the reduction of the effective area of the photovoltaic cell. Thus, the resistance of the grid lines on the front side of the photovoltaic cell is significant, and the efficiency of the photovoltaic cell is reduced through resistive heating of the grid lines during operation.